Sibling Rivalry. Jaime Roberts.pdf
Rivalry occurs between most, if not all, siblings to a varying degree. Rivalry may be manifested as a verbal or physical attack, frustration, persistent demands for attention, or as regressive phenomena. When handled properly, healthy competition among siblings will lead to the acquisition of social, interpersonal and cognitive skills that are important to the development of the child. Mismanagement of the competition may lead to psychological problems later in life. The appropriate spacing of children and the preparation of existing children for a new sibling help to reduce sibling rivalry. Family situations that will potentially lead to jealousy should be avoided. Parents should not make comparisons between siblings and favoritism should be avoided. When episodes of sibling rivalry develop, the cause rather than the manifestation of the rivalry should be treated. Patience, love, understanding, common sense, and humor are important parental skills necessary to minimize sibling rivalry.
Sibling Rivalry. Jaime Roberts.pdf
Mammal life history traits relating to growth and reproduction are extremely diverse. Sibling rivalry may contribute to selection pressures influencing this diversity, because individuals that are relatively large at birth typically have an advantage in competition for milk. However, selection for increased growth rate is likely to be constrained by kin selection and physiological costs. Here, we present and test a model examining the ESS (evolutionarily stable strategy) balance between these constraints and advantages associated with increased prenatal growth in mammal sibling rivalry. Predictions of the model are supported by results of comparative analyses for the Carnivora and Insectivora, which demonstrate an increase in prenatal growth rate with increasing intensity of postnatal scramble competition, and a decrease in postnatal growth rate relative to size at birth. Because increased prenatal growth rates are predicted to select for reduced gestation length under certain conditions, our study also indicates that sibling rivalry may contribute to selection pressures influencing variation in altriciality and precociality among mammals.
Dalbergia sissoo, a wind-dispersed tropical tree, shows a positively skewed distribution of seeds per pod. This is attributed to the enhanced dispersal advantage of few-seeded pods due to their reduced wing loading (ratio of weight to pod surface area) and low settling velocity. The proximate mechanisms causing the positively skewed distribution were investigated. The distribution could not be attributed to the distribution pattern of ovule number per ovary, pollen grain limitation, lack of ovule fertilization, or post-fertilization elimination of many-seeded pods. Rather, it was caused by the post-fertilization abortion of seeds within a pod 2 weeks after fertilization. This intra-pod seed abortion (IPSA) is due to a dominance hierarchy of fertilized ovules from the distal (near stigma) to the basal end, generated by the temporal differences in fertilization. The dominant developing seeds at the distal end cause the abortion of others through the production and diffusion of an aborting agent. When the dominance hierarchy of the siblings is not intense, pods are formed with more than one seed. We argue that the positively skewed distribution of seeds per pod is not due to maternal regulation but is a result of sibling rivalry. We propose that this sibling rivalry is generated by genetic differences in pollen grain fitness and disucss the results in the context of parent-offspring conflict.
Studied here were the links between sibling differences in trajectories of change in the qualities of parent-child relationships and the qualities of sibling relationships across a 2-year period in adolescence. Participants were first- and second-born siblings (M age = 14.94 years for firstborns and M age = 12.46 years for secondborns) from 185 predominantly White, working and middle-class families. In home interviews, siblings reported on their dyadic family relationships. For reports of parent-child warmth but not parent-child conflict, results were consistent with sibling differentiation theory: Increasing differences between siblings over time in parent-child warmth were linked to trajectories of increasing warmth and decreasing conflict in the sibling relationship as reported by firstborns, and increasing warmth in the sibling relationship as reported by secondborns. The findings support the view that sibling differentiation may be a strategy for managing sibling conflict and rivalry.
This pilot study explores the degree of solidarity felt between full and half siblings who are raised in a Mormon Fundamentalist polygamous community. The community under study is unique in that, at the level of official culture, it actively promotes full and half sibling solidarity through an ethos that strives to downplay genetic differences in favor of a harmonious family living together in one household. This community is an ideal cultural setting in which to examine the suitability of inclusive fitness theory for understanding the factors that promote family cohesion, sibling solidarity, and rivalry. Our main question becomes: is the degree of sibling solidarity a manifestation of genetic closeness or a natural byproduct of emotional closeness that arises from being raised together? We found evidence for more solidarity between full siblings than between half siblings. Our data suggest that, despite the force of religious ideals, and notwithstanding the continued close physical proximity of half siblings in the polygamous family, there is a pronounced clustering of feeling and affection in the polygamous family that is consistent with inclusive fitness theory.
Fetal microchimerism (FMc) is predicted to promote the fitness of the fetus and maternal microchimerism (MMc) to promote the fitness of the mother. Offspring and mothers benefit from each other's health. Therefore, microchimeric cells should usually not be harmful to their host. However, the evolutionary interests of mothers and offspring diverge when there is competition among siblings for maternal investment. Fetal cells in mothers' bodies could benefit their own offspring at the expense of its sibs by promoting lactogenesis or by extending the interbirth interval. Maternal cells in fetal bodies could benefit from the suppression of sibling rivalry. Non-inherited haplotypes in MMc or sibling microchimerism (SMc) gain no direct benefit from their hosts' health and could be associated with substantial detrimental effects. 041b061a72